1. Field of the Invention
The invention relates to a hoisting drive for use in the iron and steel industry.
2. Description of the Related Art
Hitherto heavy hydraulic cylinders have been used as hoisting drives in the iron and steel industry, e.g. in vibrating devices of continuous casting moulds or plug control devices in a continuous casting plant.
The use of hydraulic drive units in the hot area is not a negligible risk, however, because of flammable hydraulic fluids. Hence for some time efforts have been made to replace the hydraulic drive units in the hot area by electrical systems. Hitherto servo motors with spindle drives have been used, wherein a rotary movement is converted into a linear movement. However, limits are imposed on these drive systems by the masses to be accelerated, the system-induced vibrations and the resulting mechanical wear in the drive spindle.
When selecting a drive system it must also be taken into account that the drive must operate satisfactorily in an environment exposed to high temperatures and large quantities of dust.
The task underlying the invention is accordingly to propose an electrical hoisting drive for use in the iron and steel industry as replacement for large hydraulic cylinders.
According to the invention this problem is solved by a hoisting drive according to claim 1. A hoisting drive in accordance with the invention comprises at least one electrical linear motor and a linear guide with a carriage. Each linear motor consists of a primary part and a secondary part. All the primary parts, respectively all secondary parts, of the linear motor are mounted on the carriage. According to the invention the linear motors are integrated with the linear guide in a closed housing cooled by a cooling medium. The primary parts, respectively the secondary parts, which are not mounted on the carriage are mounted on the housing. A cylindrical hoisting rod is introduced in a sealed manner into the housing and connected mechanically to the carriage. It should be noted in this respect that electric linear motors arexe2x80x94because of their design and propertiesxe2x80x94by no means suitable for use in an environment exposed to dust and heat. Only the arrangement according to the invention will make them a suitable drive meeting the requirements for applications in the iron and steel industry. The hoisting drive according to the invention is extremely compact, unaffected by environmental factors such as heat, dust and sprayed water. It permits rapid and accurate positioning. It is extremely rugged in use, tolerates non-axial loads and does not have a sensitive mechanism, which could give rise to faults.
In a preferred embodiment the linear guide has at least one plane of symmetry, which contains the central axis of the hoisting rod. The linear motors are then arranged in pairs symmetrically with this plane of symmetry. As a result of the symmetrical arrangement of the linear motors, the forces are transmitted free of any force moment to the hoisting rod. Consequently symmetrical loading of the linear guide is ensured.
The housing advantageously has a jacket with cooling ducts, which can be connected to a cooling circuit. Such cooling ducts can be designed, for example, as bore holes in the housing jacket, preferably in the longitudinal direction of the housing. A coolant, e.g. water, flows through these cooling ducts, which cool the housing and the secondary and primary parts mounted on the housing when they are under load. Alternatively the housing can also be of double-walled construction, whereby the space between the walls can be connected to a cooling circuit.
In a further advantageous embodiment the hoisting rod has at least one duct, which can be connected to a cooling circuit. These cooling ducts through the hoisting rod allow to cool the carriage and the primary parts, respectively secondary parts, of the linear motors under load, which are mounted on the carriage.
In addition a position measuring system for the carriage can be integrated in the housing. A measuring device of this type comprises, for example, a measuring sensor mounted on the carriage. The position of the carriage and consequently also the position of the hoisting rod connected mechanically to the carriage is thus known at any time.
The position measuring system can be incorporated in a position control circuit. In this case the position control circuit consists of the position measuring system, a controller and a controllable electrical power supply system. The position of the cylindrical hoisting rod is determined via the position measuring system at specific times. The measured position value is transmitted to the controller, which compares the measured value with a predetermined set value. The controller forms the differential value from the two values. Depending on the calculated differential value the controller activates the controllable electrical power supply. The latter changes the power supply of the primary parts of the linear motors.
The hoisting drive according to the invention is used e.g. advantageously in the iron and steel industry for vibration of a continuous casting mould, as described e.g. in WO 95/03904.
Furthermore, a device of this type is suitable as an actuator drive for control of the inflow of liquid steel in continuous casting plants. These inflow control systems control the level in the distributor channel or the continuous casting mould. The actuator drive can be used both for position control of a ceramic plug in bottom-tap casting, and also for slide control systems.